JP2728502B2 - Optical integrated circuit and optical device - Google Patents

Description

The present invention relates to an optical integrated circuit and an optical device used for an optical communication or an optoelectronic device such as an optical disk recording device, particularly when a semiconductor laser is used as a light source. The present invention relates to an optical integrated circuit and an optical device in which various aberrations caused by a wavelength variation of a light source are corrected.

[Conventional technology]

2. Description of the Related Art Optical components used in fields such as optical communication systems and optical information processing have conventionally been constructed by mechanically combining bulk components such as lenses, prisms, and gratings. Therefore, the above optical components have large external dimensions and cannot meet the demand for miniaturization, are expensive, or are combined by mechanical coupling. There are various problems that the properties are inferior. Therefore, in recent years, the concept of an optical integrated circuit (optical IC) in which a plurality of elements are integrated on one substrate has been introduced, and significant miniaturization and cost reduction of optical components have been studied. That is, the optical IC is an optical component that is formed by integrating a light receiving / emitting element, a waveguide type (thin film type) lens, a grating, and the like on one substrate.

As a component of the optical IC, there is a grating coupler. This is a waveguide type diffraction grating formed in an optical waveguide, and has the function of making light incident on the optical waveguide and emitting light out of the optical waveguide. one of.

The grating coupler mentioned above is JHHarr
is, et al.Theory and Design of Periodic Cou
plers, Appl. Opt., 11, 10 (1972), T. Tamir and STP
eng, Analysis and Design of Grating Couplers, A
Ppl. Phys., 14, (1977) discusses the specific design method. Further, as an optical component which is made into an optical IC by using a grating coupler, JP-A-61-85641 and JP-A-61-296540 describe examples of application as an optical head for an optical disk device.

[Problems to be solved by the invention]

In the above prior art, when a semiconductor laser is used as a light source, there are the following problems. That is, the wavelength of light emitted from a semiconductor laser generally changes due to an operating temperature or a variation in a manufacturing process when manufacturing the semiconductor laser. Therefore, the first problem in the case where the emitted wavelength is not a single wavelength is that the incident angle that can be incident on the optical waveguide is changed by the grating coupler, and the incident coupling efficiency is reduced. Further, when the grating coupler is used on the emission side, there is a problem that the emission angle changes in the same manner as described above.

The second problem is that when a grating coupler having an irregularly-spaced curve shape is used as an objective lens of an optical head as a condensing grating coupler, the light at the focal point needs to be exposed in order to express high-density information recorded on an optical disk medium. It is necessary to narrow the spot size close to the diffraction limit.
Therefore, the lens NA (lens diameter / focal length) is 0.45.
The above is required. However, in the case of the conventional condensing grating coupler described above, when the NA is 0.45 and the wavelength shift of the laser beam is Δλ, a severe value of | Δλ | = 9.8 × 10 ⁻⁴ is required. The following values are required for the deviation δ from the optical axis of the laser beam and the deviation ΔN of the effective refractive index of the guided light, respectively.

| Δ | = 6.9 × 10 ⁻⁴ | ΔN | = 9.8 × 10 ⁻⁴ These values are extremely severe and not on a practical level. In particular, since δ is small, the surface acoustic wave propagates perpendicularly to the guided light, and the elastic wave deflects the light left and right from the optical axis. Was.

The third problem is that, in the above-mentioned conventional optical head formed as an optical IC, since the beam splitter for detecting a signal from the optical disk is configured as a so-called coplanar optical element, the acceptance angle (where light originally , The deterioration of the element characteristics is small even if the incident angle is shifted from the incident angle, the allowable deviation of the incident angle is small, the detection range of the focus error signal is narrow, and the range in which the focusing servo operates is limited. In addition, there is a problem that the characteristic deterioration with respect to the wavelength fluctuation of the laser beam is large, that is, the so-called chromatic aberration is large.

A fourth problem is that when the optical disk is not parallel to the optical head, the optical axis of the conventional optical head is shifted from the central axis of the beam splitter when light reflected on the optical disk surface is guided again to the optical waveguide. Therefore, there is a problem that an offset occurs in the tracking error detection signal.

A first object of the present invention is to provide an optical integrated circuit having a small variation in characteristics and high light use efficiency even when a multi-mode semiconductor laser beam is used.

A second object of the present invention is to provide an optical pickup that can deflect guided light from the optical axis to the left and right at high speed by surface acoustic waves, and that can access at high speed, that is, to provide an optical information reading device. . A third object of the present invention is to provide an improved optical head which operates effectively even when the wavelength of the laser beam fluctuates and a focusing servo is effectively used in a wide range. An object of the present invention is to reduce an offset of a tracking error detection signal, which becomes a problem when the optical head is inclined and not parallel to the optical head.

[Means for solving the problem]

The above object is to provide an optical integrated circuit in which a semiconductor laser is used as a light source and light emitted from the semiconductor laser is incident on an optical waveguide.
The blaze angle of the blazed laser beam incident grating coupler satisfies the following expression.

N cos α _BA = n _s (sin A ₀ sin α _BA + cos A ₀ cos α _BA ) α _BA : Blaze angle of the grating coupler for laser beam incidence A ₀ : Incident angle of the laser beam on the grating coupler N: Optical waveguide Effective refractive index n _s : Refractive index of optical integrated circuit board Also, in an optical integrated circuit in which semiconductor laser light is used as a light source and laser light guided in the optical waveguide is emitted by a grating coupler, The blaze angle of the emission grating coupler is an angle satisfying the following expression.

N cos α _BA '= _ns (sin α ₀ sin α _BA ' + cos α ₀ cos α _BA ') α _BA ': Blaze angle of grating coupler for laser beam incidence α ₀ : Incident angle of laser light to grating coupler N : Effective refractive index of optical waveguide n _s : Refractive index of optical integrated circuit board Further, as a light source, a semiconductor laser, a collimator lens for converting the light emitted from the semiconductor laser into parallel light, formed on a dielectric substrate having an acousto-optic effect Optical waveguide, a grating coupler for making light incident on the optical waveguide, an optical deflector using surface acoustic waves formed on the optical waveguide, a grating coupler for emitting deflected light from the optical waveguide, and a semiconductor laser light source. In an optical device having an aberration correction grating for correcting wavelength fluctuation and a lens provided with a focusing mechanism for condensing light on an optical disc, The reflected light from the optical disk characterized by comprising an optical detector for detecting via the cutout portion formed on the bottom surface of the substrate.

[Action]

An example of the operation and effect of the present invention will be described with reference to FIG.
The effect of the present invention is achieved by the aberration correcting grating shown in FIG. That is, in FIG.
When the wavelength of the semiconductor laser light changes from λ (0) to λ (1) (λ (0)> λ (1)), the incident angles to the grating coupler correspond to λ (0) and λ (1). α
Only in the case of (0) and α (1), strong coupling of light to the optical waveguide occurs. Here, when there is no aberration correction grating,
Since the angle of incidence on the grating coupler does not change even if the wavelength changes, the incident coupling efficiency decreases. Therefore, an aberration correcting grating is provided, and the grating interval D and the inclination angle δ are corrected. As a result, the diffraction angles from the aberration correction grating 6 can be set to specific angles γ (0) and γ (1) with respect to the light having the wavelengths λ (0) and λ (1). Note that γ (0) and γ (1) are refracted at the interface with the substrate, and the incident angles α to the grating coupler are respectively
(0), α (1). Therefore, even if the wavelength of the semiconductor laser light changes, the angle of incidence on the grating coupler can be set to α (0) and α (1) corresponding to λ (0) and λ (1), and the wavelength of the laser light It is possible to prevent the incident coupling efficiency from decreasing due to the fluctuation. Also, aberrations such as chromatic aberration can be prevented. Here, λ (0) to λ
The aberration correction grating 6 satisfies the Bragg condition for at least one wavelength of the light of (1), or
Defining D so that diffraction occurs near the ragg condition is important for obtaining high-intensity light, and is one of the points of the present invention.

Example 1 Next, an example of the present invention will be described more specifically with reference to the drawings.

In FIG. 1, a LiNbO ₃ crystal is used as a substrate 1, and an optical waveguide 2 and a grating coupler 3 having a refractive index slightly higher than that of the substrate are formed near the substrate surface. Next, glass blocks 5 and 5 'for allowing the emitted light of the semiconductor laser 4 to be incident on the substrate 1 in parallel to the glass blocks 5, 5'.
An aberration correction grating 6 is interposed between 5 '.

Next, the operation of the optical integrated circuit according to the present invention shown in FIG. 1 will be described. In FIG. 1, a grating coupler 3 is a linearly-spaced diffraction grating. The grating interval is Λ, the effective refractive index of the optical waveguide 2 is N, and the refractive index of the substrate 1 is
Assuming that n _s , the wavelength of the semiconductor laser 4 is λ, and the incident angle of the laser beam on the grating coupler 3 is α, According to the relationship, the incident angle α is uniquely determined with respect to the wavelength λ. Therefore, in the present invention, an aberration correction grating 6 is provided to prevent a decrease in the coupling efficiency even if the wavelength of the semiconductor laser 4 changes. That is, when the wavelength of the semiconductor laser 4 changes from λ (0) to λ (1) (λ (0)> λ (1)), the aberration correcting grating 6
, The lattice spacing D and the inclination angle δ are corrected. As a result, the wavelength λ
The diffraction angles of the light of (0) and λ (1) from the aberration correction grating 6 are given angles γ (0) and γ (1).
Can be set to Therefore, even if the wavelength of the semiconductor laser 4 changes, the incident angle of the grating coupler is changed to λ.
Α (0) and α (1) corresponding to (0) and λ (1) can be obtained, and it is possible to prevent the incidence coupling efficiency from decreasing due to the wavelength fluctuation of the laser beam and aberrations such as chromatic aberration. next,
A specific example of the grating interval D and the inclination angle δ of the aberration correcting grating 6 will be described.

First, D is set to a condition that satisfies the equations (2) and (3) so that the light having the wavelength λ (0) is diffracted by the aberration correcting grating 6 at or near the Bragg condition.

β (0) ≒ γ (0) (3) β (0): incidence angle with respect to the diffraction grating at wavelength λ (0) γ (0): emission angle with respect to the diffraction grating at wavelength λ (0) and wavelength The condition satisfying the expression (4) is set so that the light of λ (1) is diffracted near the Bragg condition.

β (1): incidence angle with respect to the diffraction grating at the wavelength λ (1) (β (0) = β (1)) γ (1): emission angle with respect to the diffraction grating at the wavelength λ (1) D, δ, θ are determined so that the expressions 5) to (12) are satisfied.

γ (0) = α ₂ (0) −θ−δ + π (11) γ (1) = α ₂ (1) −θ−δ + π (12) α ₀ (0): grating coupler at λ (0) incidence angle alpha ₀ to (1): λ (1) an incident angle alpha ₁ of the grating coupler in the (0): lambda refraction angle from the glass block to the substrate in _{(0) α 1 (1)} : λ ( Angle of refraction of the substrate from the glass block in 1) α ₂ (0): Angle of incidence on the substrate at λ (0) α ₂ (1): Angle of incidence on the substrate at λ (1) Λ: Grating coupler Lattice spacing D: Lattice spacing of aberration correcting grating 6 θ: Cutting angle of substrate end face δ: Slope of aberration correcting grating 6 m: Diffraction order of light diffracted by aberration correcting grating 6, I do.

N: the optical waveguide 2 of the effective refractive index n _s: the refractive index n _P of the substrate 1: Figure 2 the refractive index of the glass block used in the present invention the aberration correcting grating 6
In order to obtain high intensity diffracted light, it is desirable to use a diffraction grating having a shape that satisfies the Bragg condition described above.

As a specific example of a diffraction grating that satisfies the conditions described above, a semiconductor laser having λ (0) of 0.78 μm and λ (1) of 0.776 μm is used, and a LiNbO ₃ crystal having n _s = 2.2 and N = 2.29 is used. Using the Ti diffused optical waveguide used, a grating coupler of Λ = 4 μm is formed on it, and the basic laser light incident end face
When a glass block made of BK-7 with n _P = 1.45 is attached, θ is about 56 degrees, δ is about 100 degrees, and D is about 1.6 μm.
In this case, the incident angles of the light of λ (0) and λ (1) with respect to the diffraction grating are equal, but the difference between the outgoing angles is about 0.1 degree, and the angle α satisfying the coupling condition to the optical waveguide at each wavelength.
₀ (0) and α ₀ (1). In this case, the efficiency of the diffracted light (the light emitted from the aberration correcting grating 6) is about T
By setting it to 11 μm, it becomes 90% or more.

Note that, as an example of the above-described aberration correcting grating 6, BK-7 glass 8 is used as a substrate, and SiO ₂
Was formed to a thickness of about 11 μm by a known film forming method such as a CVD method, and the SiO ₂ layer was finely processed into a predetermined shape by known photolithography. Then, BK-7 made of glass blocks 5, 5 'of the diffraction grating 6 bonded with an adhesive having substantially the same refractive index as BK-7, to form a periodic structure in SiO ₂ 9 and the adhesive agent described above This allows the grating to function as the aberration correcting grating 6.

As a form of the diffraction grating used in the present invention, there is a reflection type diffraction grating provided with a reflection film 10 as shown in FIG. 3 in addition to the transmission type diffraction grating as shown in FIG. 1 and FIG.

FIG. 4 shows an embodiment of the present invention, which is an optical IC effective as an optical head used in an optical disk device. In FIG. 4, the light emitted from the semiconductor laser 4 enters the grating coupler 3 from the substrate 1 side via the collimator lens 11, the glass block 5, and the aberration correcting grating 6, and is guided to the optical waveguide 2. The guided light 7 is deflected by an optical deflector 12 utilizing a surface acoustic wave (SAW) formed on the optical waveguide 2, is emitted again into the substrate by a grating coupler 3 'on the emission side, and is diffracted by an aberration correction grating 6'. After the optical path is changed vertically by the glass block 13, the light is focused on a point on the optical disk 15 by the objective lens 14. On the other hand, the reflected light from the optical disk 15 follows the same path again, is guided to the optical waveguide 2 by the exit-side grating coupler 3 ', passes through the optical deflector 12, and is formed on the optical waveguide 2 by the condensing beam splitter. The light is divided into two by 16 and emitted to the substrate side, and is focused on one point of the light receiving surface of the photodiodes 17 and 17 ′ provided on the end face of the glass block 5, and the signal from the optical disk 15 is detected.

Hereinafter, a method of manufacturing the optical IC of FIG. 4 and details of its operation will be described. First, regarding the manufacturing method of the optical IC shown in FIG. 4, first, the grating couplers 3, 3 'and the condensing beam splitter 16 are used.
Various types of waveguide type optical elements will be described with reference to FIG. In FIG. 5, LiNb optically polished as the substrate 1
Using an O ₃ crystal, Ti was deposited to a thickness of 24 nm by sputtering, and thermal diffusion was performed to form an optical waveguide 2. The sputtering conditions were as follows: high frequency power 300W, argon gas pressure
0.35 Pa, sputtering rate 0.4 nm / sec. The thermal diffusion was performed by using an electric furnace, heating to 1000 ° C., flowing an argon gas atmosphere for 2 hours, and subsequently flowing an oxygen gas for 0.5 hours. Here, the surface refractive index of the optical waveguide is n _f = 2.22, and the equivalent refractive index N = 2.
209 TE single mode optical waveguides. Optical waveguide 2
May be prepared by a proton exchange method. Optical waveguide 2
The buffer layer 18 formed on the top is for preventing peeling and cracking of the grating layer to be formed next, and is used for sputtering Corning 7059 glass by sputtering.
nm formed. The sputtering conditions were a high frequency power of 100 W, an argon gas pressure of 0.35 Pa, and a sputtering rate of 0.2 nm / sec. TiO ₂ was formed as a grating layer 3 on the buffer layer by reactive sputtering to a thickness of 100 nm. The sputtering conditions were TiO ₂
Using argon and oxygen as sputtering gas with a target, O ₂ and Ar flow ratio 0.7, sputtering gas pressure 0.42 Pa,
The high frequency power is 500 W and the sputtering speed is 0.1 nm / sec. Next, in order to finely process the grating layer 3 and the buffer layer 18 into a predetermined waveguide type optical element, a resist 19 was formed on the grating layer 3 by a spin coating method. Here, chloromethylated polystyrene (CMS-EXR: manufactured by Toyo Soda), which is an electron beam resist, was used as the resist 19, and had a thickness of 0.5 μm. After pre-baking the resist at 130 ° C. for 20 minutes, an electron beam 20 was applied to a predetermined grating layer shape. Irradiation condition is electron beam diameter 0.1
μm and the irradiation amount was 16 μc / cm ² . After the electron beam exposure, development was performed to form a resist mask. Thereafter, the grating layer 3 and the buffer layer 18 are formed by ion etching.
Was finely processed. The conditions of the ion etching were as follows: CF ₄ was used as an etching gas, pressure 3.8 Pa, high frequency power 200 W,
The etching time was 15 minutes. After etching, the resist mask was removed, and various waveguide-type optical elements such as the grating couplers 3 and 3 'and the converging beam splitter 16 were formed. Next, the SAW optical deflector 12 is made of Al by vacuum evaporation.
The film was deposited to a thickness of 100 nm and finely processed into a predetermined comb-shaped electrode.
In addition, the said process used the lift-off method. The specifications of the electrodes are a center wavelength of 14 μm, a center frequency of 250 MHz, and a logarithm of 2. Next, with regard to the aberration correcting grating of No. 6, BK-7 glass was used as the substrate 8, and SiO ₂ 9 was coated thereon with about 11 μm and SiCl _4.
It was formed by CVD or vapor deposition using sputtering and O ₂ as raw materials, sputtering, or the like. Next, in order to process the SiO ₂ 9 into a predetermined lattice shape by photolithography, was similar to the various waveguide type optical element having the above-described photoresist to (OFPR 800) is formed by 1μm spin coating. 85 ℃ above resist
After pre-baking for 30 minutes, exposure was performed in close contact with a photomask depicting a predetermined lattice shape using a UV exposure apparatus. After the exposure, the film was immersed in chlorobenzene at 40 ° C. for 5 minutes and developed. Cr is vapor-deposited on the grid pattern made of resist, and ultrasonic cleaning is performed in acetone to remove the resist.
A Cr mask was formed. Thereafter, SiO ₂ was finely processed by ion etching using CF ₄ gas, and Cr was removed to form a lattice pattern. This photolithography technique can also be applied to the above-described fine processing of the grating layer and the buffer layer. The substrate 1, on which the above-described elements are formed,
Gratings 6, 6 'for aberration correction and glass blocks 5, 5' made of BK-7 are cut at their respective end faces at a predetermined angle.
It was polished and bonded with an adhesive having a refractive index almost the same as that of BK-7, and the semiconductor laser 4 and the photodiodes 17, 17 'were end-face-bonded to form the optical IC shown in FIG. Next, the optical IC shown in Fig. 4
The operation of will be described. Light emitted from the semiconductor laser 4 (wavelength 0.776 to 0.78 μm) is converted into parallel light by the collimator lens 11, diffracted by the aberration correcting grating 6, further refracted at the interface of the substrate 1, and has a wavelength and a lattice spacing of the grating coupler. Is guided to the optical waveguide 2 according to the equations (10) and (11). The guided light 7 is deflected by the SAW light deflector 12, and is deflected by the grating coupler 3 '.
And exits the substrate according to the equations (10) and (11) according to the wavelength and the grating interval of the grating coupler. The light emitted into the substrate is diffracted by the aberration correcting grating 6 ', reflected by the end face of the glass block 13, emitted upward, and condensed by a lens 14 having a mechanism for moving vertically to the optical disk 15. Focused on 15 pits (information). The light reflected by the optical disk 15 passes through the lens 14, the glass block 13, and the aberration correcting grating 6 ', is incident on the optical waveguide 2 again by the grating coupler 3', and is then split into two by being incident on the converging beam splitter 16. At the same time, the light is condensed on the two-division photodiodes 17 and 17 ', and the bit information is read.

Here, in the case where the aberration correcting grating 6 is not provided, when the wavelength of the semiconductor laser changes in the range of 0.776 to 0.78 μm, the angle at which the coupling to the optical waveguide 2 occurs with the maximum efficiency is about 0.
Although it changes by one degree, the incidence coupling efficiency is reduced because the angle of incidence on the grating coupler 3 is always constant. On the other hand, by using the aberration correcting grating 6 of the present invention having the grating pitch D of about 1.6 μm and the grating height T of about 11 μm, the diffraction is performed at different angles depending on the wavelength, and the grating coupler 3 is formed at the optimum angle. And high incident coupling efficiency is obtained.

When the grating 6 'for aberration correction is not provided, when the wavelength of the semiconductor laser changes in the range of 0.776 to 0.78 µm, the incident angle to the lens 14 differs by about 0.1 °, and the spot device shifts by about 8 µm in the jitter direction. On the other hand, by using the aberration correcting grating 6 'of the present invention having the grating pitch D of about 2.5 μm and the grating height T of about 11 μm, the difference in the incident angle becomes less than 0.01 degree and the spot in the jitter direction becomes smaller. The position fluctuation also becomes 0.01 μm or less. The wavelength dependence of spot position fluctuation on the optical disk is greatly reduced by the aberration correcting grating 6 'of the present invention, and an optical head from which more accurate information can be read.

The material of the optical IC is quartz, SiO ₂ glass substrate, dielectric crystal substrate, SiO ₂ glass optical waveguide, metal diffusion optical waveguide, and chalcogenide glass , TiO ₂ , ZnO, ZnS, 6 As a material for forming a grating for aberration correction, SiO ₂ glass, a polymer compound, and as a glass block forming material for 10, SiO ₂
There are ₂ types of glass, etc., and all materials generally used for forming optical elements, optical waveguides, and thin film optical elements can be used. Using these materials, lithography techniques used in the manufacture of semiconductors, vacuum An element can be formed by using the technique. Further, the above-described optical head formed into an optical IC can be applied as an optical head for a laser beam printer.

Embodiment 2 FIG. 6 shows a second embodiment of the present invention.

In the figure, 1 is a dielectric or glass substrate, 2 is formed on a first main plane of the substrate 1, an optical waveguide having a higher refractive index than the substrate 1, and 3 'is formed on the optical waveguide 2. Grating coupler having an evenly spaced linear shape, 7 is a guided light propagating in the optical waveguide 2, 6 'is a grating for correcting aberration, 14 is a lens for condensing light emitted from the substrate,
Reference numeral 21 denotes a focal point of light emitted from the lens (hereinafter referred to as a focal point for convenience). Note that the guided light 7 needs to be collimated parallel light.

Here, the wavelength of the laser light source lambda, the effective refractive index for the guided light 7 of the optical waveguide 2 N, an n _s the refractive index of the substrate 1, the lattice spacing of the grating coupler 3 'on uniform linear form Λ And In order to emit m-order light in the direction of the substrate in the direction of the angle θ with respect to the substrate surface using the grating coupler 3 ′, It is necessary to satisfy the condition. Usually, -1 order light is used as the diffracted light.

In addition to conditional expression (13), Is satisfied, the guided light is emitted only in the direction of the substrate and not emitted into the air, so that a large efficiency can be obtained.

The lattice spacing Λ is given as follows, where m = −1 and θ = 30 degrees.

As an example, as the substrate 1, LiNbO _{3 with} n _s = 2.177
The optical waveguide 2 is manufactured by thermal diffusion of Ti using
Assuming that 2.187 is used and a semiconductor laser of λ = 0.78 (μm) is used as a light source, Λ = 2.59 (μm), which can be sufficiently manufactured using photolithography technology. Also,
At this time, since the condition (14) is also satisfied, the guided light can be efficiently emitted only in the substrate direction.

Further, Pyrex glass with n _s = 1.472 was used as the substrate 1, and Corning 7059 glass with a refractive index of 1.544 formed by sputtering was used as the optical waveguide 2, and N = 1.520
Assuming that a semiconductor laser of λ = 0.78 (μm) is used as the light source, Λ = 3.18 (μm), which can be sufficiently manufactured by using the photolithography technique. At this time, since the condition (14) is also satisfied, the guided light can be efficiently emitted only in the substrate direction.

As described above, in the optical integrated circuit according to the present invention, greater efficiency can be obtained as compared with the conventional one.

On the other hand, the aberration when the laser light wavelength shift Δλ, the effective refractive index shift ΔN, and the shift δ of the laser light from the optical axis occur are as follows.

As shown in FIG. 7, the propagation direction of the light beam when δ = 0 is z
Take a left-handed linear Cartesian coordinate system such as an axis,
A left-handed linear orthogonal coordinate system is used in which the origin of the light is the origin and the direction in which the light beam exits when z = 0 is the z 'axis.
The origins of the two coordinate systems are matched. The z axis and the z 'axis form an angle of θ.

First, when incident parallel light is incident in a direction shifted by δ from the z-axis, the phase matching condition in the xyz system is Becomes Here, k _o = 2π / λ, and Px, Py, and Pz are components of the emission vector in the xyz system. xyz system and x'y'z '
The system vector is transformed Therefore, the output vector is, in the x′y′z ′ system, Becomes Assuming that the angle between the direction of the emitted light and the z ′ axis is φ, in the case of using LiNbO ₃ as the substrate, | δ |
In the range of 0.01 (rad), it is approximately | δ | Further, due to the effect of refraction at the interface between the substrate and air, the diameter becomes φ〜2 | δ | in air. That is, the guided light is z ′
The light is emitted as parallel light in a direction inclined approximately 2δ from the axis.

When an ordinary objective lens for an optical pickup is used as the condensing lens 14, since the emitted light is parallel light, if δ is sufficiently small as described above, the aberration is small enough to cause almost no problem.

Further, for example, if the focal length of the lens is 3 mm, the focal point 21 moves about 30 μm when δ to 0.01, so that the guided light 7 is actively excited by the SAW (surface acoustic wave) optical deflector 12.
By using AW to deflect by δ, access and tracking correction for several tracks can be performed as shown in FIG.

As described above, by making the shape of the grating coupler a straight line, a pickup objective lens system that is strong against deflection of the guided light 7 from the optical axis z can be configured.

On the other hand, when the effective refractive index shift ΔN and the wavelength shift of the laser light source occur, the emitted light direction is shifted by an angle Δθ on the xz (x′z ′) plane. However, the outgoing light is parallel light. Its size is almost Can be expressed as ΔN, when Δλ occurs alone, in the case of using the LiNbO ₃ as a substrate, It is. Considering the effect of refraction, | Δθ | <0.01 (ra
d) This is a value that is sufficiently larger than the conventional one.

As described above, in the optical integrated circuit of the present invention, since a linear diffraction grating is used for the grating coupler,
Even if Δλ, ΔN, and δ are extremely large, the outgoing light is parallel light. Therefore, if a high-performance pickup objective lens is used, the generated aberration can be reduced.

Embodiment 3 FIG. 9 shows an optical integrated circuit according to a third embodiment of the present invention. FIG. 9 (a) is a sectional view, and FIG. 9 (b) is a plan view. .

In the figure, 1 is a substrate made of an optical material such as lithium niobate (LiNbO ₃ ) having a refractive index of 2.177, and 2 is an optical waveguide having a higher refractive index than the substrate. In this example, titanium is deposited on a lithium niobate substrate. Heat diffusion of titanium, about
An optical waveguide of 1.5 μm was formed. Reference numeral 3 'denotes an evenly spaced linear grating coupler formed on the optical waveguide.
It is formed of an optical material having a higher refractive index than the optical waveguide. In this example, a titanium oxide (TiO ₂ ) film having a refractive index of 2.4 is formed on the optical waveguide, and a linear grating having a pitch of 2.59 μm is formed by a lithographic pattern forming technique. The coupler was formed over 4 mm in the light traveling direction. 22 is a lens means provided in front of the diffraction grating 3 'on the optical waveguide 3.
In this example, a transmission type Fresnel lens having a diameter of about 2 mm was formed on the optical waveguide 2 by a known technique. The aperture of the lens is equal to or larger than the width of the guided light. The lens may be another bulk lens, but a Fresnel lens is preferable because it is integrated on a substrate and has a compact configuration. Reference numeral 23 denotes an end surface of the substrate, which is a reflection surface cut and polished at an angle of 30 degrees with respect to the surface of the substrate.
Is formed to be equal to the emission angle θ. 21 is the focal point of light f
It is. The guided light 7 shown in FIG. 9B is a collimated parallel light.

Here, the thickness of titanium oxide (TiO ₂ ) constituting the diffraction grating, the focal length f of the Fresnel lens, and the aperture D will be described in more detail. When the Fresnel lens is used as the objective lens of the optical pickup head, the numerical aperture NA Must be 0.5. The effective numerical aperture of this lens is
It is determined by the numerical aperture of the diffraction grating. Now, as shown in FIG. 9B, the opening length of the diffraction grating in the x direction is Lx, and the opening length in the y direction is Ly. When the light emitted by the diffraction grating is emitted in a direction forming an angle of θ with the surface of the substrate 1, the area of the light beam incident on the Fresnel lens 22 is Lx cos θ × Ly. For example, if θ = 30 degrees and f = 2 mm as in this embodiment, it is necessary to set Lx = 2.30 mm and Ly = 1.15 mm. At this time, the aperture D of the Fresnel lens
Is to cover the entire luminous flux Needs to be

The amplitude of the light emitted from the grating coupler 3 'is emitted in the x-axis direction with a dependency of exp (-. Alpha.x). Here, α is called a radiation loss coefficient. In order to secure a numerical aperture, a condition of αLx1 is required. In the above example, The value of α is determined by the refractive index and thickness of the substrate 1, the optical waveguide 2, and the grating coupler 3 '. As described above, the refractive index n _s
LiNbO ₃ = 2.177, refractive index N of the optical waveguide 2 = 2.187, and T of refractive index _ng = 2.4 as a loading layer material of the grating coupler.
When iO ₂ is used, the thickness of TiO ₂ may be about 30 nm in order to set α to 0.4.

Returning again to the description of the optical integrated circuit having the configuration shown in FIGS. 9A and 9B, the parameters of each optical system will be examined.

Here, a light source wavelength of the laser beam (FIG omitted in) lambda, the effective refractive index of the optical waveguide 2 N, the refractive index of the substrate 1 n _s,
The lattice spacing of the equally-spaced linear grating coupler 3 'is denoted by Λ.

Assuming that the angle between the incident direction of the light emitted by the grating coupler 3 'and the normal direction of the polished surface 23 of the substrate end surface is φ, total reflection occurs when n _s sin φ> 1 (22). In the case of the present embodiment, n _s = 2.177,
Since φ = 30 (degrees), it is included in the range expression (22) in which total reflection occurs.

Next, the focal length of the Fresnel lens 22 is f, and a coordinate system as shown in FIG. The formula of the Fresnel lens is Given by Since this Fresnel lens is axially symmetric with respect to the optical axis, the lowest order of aberration is the third order. The third-order wavefront aberration function is described in, for example, Meier's reference, J. Opt. Sco. Amer., Vo
As discussed in l.55, No. 8 (1965), pp. 987-992,

Here, x = rcosθ and y = rsinθ were displayed in polar coordinates. Λ ′ is the actual wavelength of the light source.

In the case of the present embodiment, the fifth-order and higher aberrations are ignored as being sufficiently small, and allowable upper limit values of Δn, Δλ, and δ that satisfy the Marechal condition are obtained. That is, the upper limit of | Δn |, | Δλ |, | δ |

Comparing the value of the prior art described above with (25), the expression (25), which is the upper limit of the present embodiment, is significantly relaxed compared to the conventional grating coupler having a light-collecting action. Also, although | Δn | is slightly inferior to that of a hybrid condensing grating coupler using a conventional condensing bulk lens, | δ | and | Δλ | are improved. If | Δλ | in the equation (25) is allowed, the practical wavelength variation is allowed up to ± 4 (nm) when a semiconductor laser having a wavelength λ = 0.78 (λm) is used. Level. Regarding | Δn |, when LiNbO ₃ having a refractive index of n _s = 2.177 is used as a substrate and guided light 7 having an effective refractive index of N = 2.187 is used, the actual effective refractive index variation is 0.0035, which is the thermal diffusion. There is no problem because normal processes such as film formation and film formation can be sufficiently controlled.

Embodiment 4 FIG. 10 is a plan view showing a fourth embodiment of the present invention, and FIG. 11 is a side view, in which an optical head according to this embodiment is an optical substrate such as a dielectric or glass. An optical waveguide 2 having a higher refractive index than that of the substrate formed on the surface of the substrate 1, a semiconductor laser LD for injecting a laser beam into the optical waveguide 2, and a diffraction grating having a group of irregularly spaced curves on the optical waveguide 2. And
The incident grating coupler 43 for guiding the emitted light of the semiconductor laser to the optical waveguide 2 and the diffraction grating 6 for aberration correction
, A pair of equal-spaced straight-line grating couplers 3 ′ formed on the optical waveguide 2 and a Fresnel lens 22 composed of concentric groups of diffraction gratings, and propagated through the optical waveguide 2. The laser beam (the traveling direction of the light is indicated by an arrow) is emitted into the substrate outside the optical waveguide 2 at an emission angle θ, and is totally reflected by the end face 23 thereof. 4
(Refer to FIG. 15) A Fresnel lens 22 for condensing a light beam at one point above, and the reflected light from the disc guided to the optical waveguide 2 by the Fresnel lens 22 is transmitted to the optical waveguide 2 through the central optical axis of the reflected light. Two pairs of nearly symmetric 4
A beam splitter 24a that divides the light into four light beams and collects the light beams
24d and photodetectors 25 and 25 'each comprising a photodiode which receives reflected light from an information recording surface (disk) divided into four by a beam splitter and converts the reflected light into an electric signal.
And a surface acoustic wave generation electrode 12 formed between the condensing grating coupler and the beam splitter and deflecting the laser light by the surface acoustic wave. In addition,
The intervals between the diffraction gratings constituting the beam splitters 24a and 24b are narrowed according to the traveling direction of light. Also, the substrate
1, the photodetectors 25 and 25 ', the semiconductor laser LD, and the like are mounted on a metal stage 26 made of, for example, aluminum.

Next, the operation of the optical head based on the above configuration will be described. First, the laser light from the semiconductor laser LD is guided to the optical waveguide 2 by a collimating means including an incident grating coupler 43 and a diffraction grating 6 for correcting aberration, and is converted into parallel light. Here, a design method of the incident grating coupler 43 and the aberration correcting grating 6 will be described. Considering the two diffraction gratings as transmission holograms, a phase transfer function for converting the divergent light of the LD into parallel light is calculated for each diffraction grating. Next, the wavelength dependence of the phase transfer function described above is examined, and the phase transfer function is determined again for each diffraction grating so that the change in the diffraction angle due to the wavelength change is canceled by each diffraction grating.

Next, the collimated laser light propagates through the optical waveguide 2 and is emitted into the substrate 1 outside the optical waveguide 2 by the grating couplers 3 ′ of equal-spaced straight lines (in this case, 30 °).
), Totally reflected by the end face 23 of the substrate, and again
, And transmitted therethrough, and the light beam is condensed by the Fresnel lens 22 at one point on the disc (not shown).

When the laser light emitted by the semiconductor laser LD passes through the beam splitters 24a and 24b and propagates in the direction of the Fresnel lens 22, it does not satisfy the Bragg diffraction condition and is not diffracted by the beam splitters 24a and 24b. The laser light focused on the optical disk is scattered or reflected depending on the presence or absence of a signal pit. The laser beam reflected by the disk (the arrow indicating the optical path is the opposite direction) is again guided into the optical waveguide 2 by the above-mentioned grating couplers 3 'at equal intervals. The guided laser light is divided by the beam splitters 24a and 24b into four pairs of substantially symmetric four light beams with respect to a plane passing through the central optical axis in the traveling direction of the laser light and perpendicular to the optical waveguide 2. The four-divided laser light is emitted into the substrate 1 at a predetermined angle, becomes convergent laser light 27a, 27b, is emitted from the end face 28, and is sent to the four-divided photodetectors 25, 25 ', respectively. The light is converted into an electric signal in the light detectors 25 and 25 '. The angle of the reflected light emitted from the beam splitters 24a and 24b to the substrate 1 can be uniquely set by setting the pitch of the diffraction grating constituting the reflected light to a predetermined value. Can be uniquely set by setting the curvature of the diffraction grating.

The optical deflector 12 using the surface acoustic wave is not essential, but by changing the frequency of the applied sound wave, the guided light transmitted through the optical waveguide can be easily deflected, and the optical path positioning is performed. It is effective for fine adjustment of.

FIGS. 12, 13 and 14 show the photodetectors 25 and 25 'divided into four photodiodes 25FA, 25FB, 25'FA, 2 respectively.
Focused spots 29F, 29'F, 29T, 29'T on the receiver 25, 25 'surface when composed of 5' FB, 25TA, 25TB, 25 'TA, 25' TB
And the focal position of the laser light emitted from the grating coupler 3 '. That is, it shows whether the focus of the laser beam is on the surface of the optical disk 15, that is, the principle of so-called focusing error signal detection. FIG. 12 shows the case where the focus is on, FIG. 13 shows the case where the optical disk 15 is before the focus, and FIG. 14 shows the case where the optical disk 15 is after the focus. The information recorded on the surface of the optical disk 15 includes the photodiodes 25FA, 25FB, 25'FA, 25'FB, 25T.
A, 25TB, 25'TA, 25TB 'respectively P _FA to output, P _FB, P _FA',
If P _FB ′, P _TA , P _TB , P _TA ′, P _TB ′, the sum P _A + P _B + P
It can be read by the _{A '+ P B' + P} TA + P TB + P TA '+ P TB'. Whether the focus error signal focus of the laser light emitted from the light condensing grating coupler is on the surface of the disk 15 _{(P FA + P FB ')} - are obtained by _{(P FB + P FA')} . The tracking error signal is ( _PTA + _PTB )-
( _PTA '+ _PTB '). As described above, the light-converged spots 29F and 29F on the photodiodes A and B divided into four parts
A focus error detection signal and a tracking error detection signal are obtained by utilizing the fact that the imaging points of T, 29'F, and 29'T move on the light receiving surface.

Next, a method for manufacturing the beam splitter 24 in the optical head of the present invention will be specifically described. Beam splitter 24
Is a diffraction grating of irregularly spaced curves formed on the optical waveguide 2. The shape equation of this diffraction grating is obtained as a hologram of a plane wave and a spherical wave converging on the photodetectors 25 and 25 '. Can be That is, if the coordinate axes x and y are as shown in FIG. 10, the pair of beam splitters 24a is symmetric with respect to the y-axis. It is. Where N is the effective refractive index of the optical waveguide 2 and n is the substrate 1
Is an integer indicating each curve. In the equation (26) according to the present embodiment, this equation is derived so that the curve passing through the point of x = y = 0 becomes m = 0. Further, f is the focal length, λ ₀ is the wavelength of the laser light in a vacuum, θ and ψ are angles formed by a straight line xy plane connecting the convergence point of the laser light and the origin, and this straight line is formed on the xy plane. The angle formed by the projected straight line and the y-axis. The diffraction grating composed of the curve group represented by the equation (26)
Patterning using an electron beam lithography system as described above,
It was manufactured by a known etching technique. In this embodiment, the average grating interval (pitch) is a diffraction grating made of TiO _2.
A pair of beam splitters 24a having a size of 3 μm and a length L of 1.6 mm was prepared. The same applies to the production of the beam splitter 24b having different imaging points. In forming the diffraction gratings constituting the beam splitters 24a and 24b,
When patterning on a resist using an electron beam lithography system, the irradiation amount of the electron beam is changed stepwise in drawing one curve, and this is repeated substantially periodically to draw all the curves. The shape can be formed in a sawtooth shape. By etching using the resist patterned in this manner, a diffraction grating having a cross-sectional shape formed by a group of curves represented by Expression (31) can be obtained.

12th, 13th, showing the principle of detecting the focusing error signal
As can be seen from FIG. 14, when there is no disc at the focal point of the Fresnel lens 22 or the objective lens 14, the reflected light from the disc that has entered the optical waveguide 2 again through the Fresnel lens 22 or the objective lens 14 is a parallel light. is not. However, the beam splitter of the optical head according to the present invention uses the optical waveguide 2
It is not a conventional coplanar type element that divides and condenses laser light in the plane of the above, but a configuration in which laser light divided into four outside the optical waveguide 2 is converged, so that the acceptance angle is large,
Even when a laser beam that is not a parallel beam is incident, the Bragg diffraction condition is satisfied and the laser beam works effectively. Other manufacturing processes were performed in the same manner as in Example 1.

Fifth Embodiment In the fifth embodiment, in the integrated optical head described in the first embodiment, a proton exchange optical waveguide having a high threshold of optical damage and a high light deflection efficiency is used as a method of manufacturing the optical waveguide 2. The present invention relates to an optical integrated circuit used.

Hereinafter, a method for producing the above-described proton exchange optical waveguide will be described in detail.

One surface of the xcut LiNbO ₃ crystal wafer is optically polished to about 1/10 of the used laser light wavelength λ. It is desirable that the transition metal impurity concentration of the crystal substrate be as low as possible. The optical damage threshold value is for a transition metal concentration in the substrate, for example, a substrate having a concentration of iron (Fe) of about 1 ppm. In a commercially available high-purity LiNbO ₃ substrate, the concentration of Fe is about 0.05 ppm. It has been confirmed that the use of the high-purity LiNbO ₃ substrate increases the threshold value of optical damage by about one digit.

After optical polishing, the substrate was subjected to ultrasonic cleaning in trichlene, isopropyl alcohol, ethanol, and pure water, and then dried by blowing nitrogen.

Next, ion exchange in which the above-mentioned substrate was subjected to a proton exchange treatment was carried out in a quartz container. Weak acids of the proton exchange source include carboxylic acids such as benzoic acid, and phosphoric acids such as pyrophosphoric acid. In the present invention, a mixture of benzoic acid and lithium benzoate was used. The substitution rate x of Li ⁺ and H ⁺ in the optical waveguide is closely related to the mixing ratio M of benzoic acid and lithium benzoate. Here, M is defined by the following equation.

As a result of the study, it was confirmed that x depends only on M regardless of the proton exchange temperature and the proton exchange time. In order to set the optimum range of x to 0.4 <x <0.55, M is set to xcutLiN
When a bO ₃ substrate was used, it was found that M should be set to 2.5. Therefore, in this example, 4.802 g of lithium benzoate and 178.605 g of benzoic acid were put into a quartz container, mixed well, and heat-treated at 245 ° C. for 5 hours. After the heat treatment, the substrate taken out of the quartz container was ultrasonically cleaned with ethanol and pure. In order to check the optical characteristics of the obtained optical waveguide, He-Ne laser light having a wavelength of 633 nm was propagated in the y direction in the optical waveguide by a rutile prism, and the optical waveguide was in a single mode. The effective refractive index was 2.2642. In addition, the light propagation loss was examined by the ordinary two prism method, and as a result, 1 dB / cm
Good value was obtained. The threshold value of the optical damage was a good value of 750 W / cm ³ with He-Ne laser light.

Next, a comb-shaped electrode for surface acoustic wave excitation was formed on the substrate subjected to the proton exchange treatment. XcutLt of this embodiment
The surface acoustic wave propagation velocity in the Z-direction propagation of NbO ₃ was 3500 m / s, and the electrode pitch was 2.9 μm so that the center frequency f ₀ was 300 MHz. The deflection angle at f ₀ = 300MHz is about 30mra
d. The logarithm N is 8 when the electrode length L is 2.8 mm.

In order to examine the characteristics of the obtained optical deflector, measure the radiation conductance using a network analyzer, measure the effective electromechanical coupling coefficient K, and compare it with the one fabricated on a bulk substrate without proton exchange treatment did. As a result of the measurement, in the case of the surface acoustic wave excitation electrode fabricated on the proton exchange optical waveguide of this example, the effective value of K was about 70% of that fabricated on the bulk substrate, and no significant deterioration was observed. Was. For reference, an electrode for exciting surface acoustic waves propagating in a direction other than the z-direction was fabricated on the proton-exchanged optical waveguide fabricated under the conditions of this example, and the effective value of k was measured in the same manner. As a result, it was found that the value of k was small in the case of propagation in the y direction.

Embodiment 6 FIGS. 15 to 18 show a sixth embodiment of the present invention. here,
As described above, in the present invention, a waveguide grating formed on an optical waveguide is used as a grating coupler for causing a semiconductor laser beam to enter the optical waveguide. As a constituent material of the grating coupler, a dielectric such as TiO ₂ , SiO ₂ , or Si—N can be used, or the optical waveguide itself can be grooved. The cross-sectional shape may be generally a rectangle as shown in FIG. 15, but in this case, the ratio of the width of the grating Λa to the lattice spacing Λa in FIG. 15 and the width Λb of the region without the grating, that is, Λa / Λb, If it deviates from 1, there is a problem that the incident coupling efficiency of the semiconductor laser light to the optical waveguide is reduced. As a method of solving this, there is a method of blazing the cross-sectional shape of the grating coupler as shown in FIG. Blazing means making the cross-sectional shape of the grating substantially triangular, and the most preferable triangle is a right triangle. Assuming that the angle between the optical waveguide surface of the right triangle and the optical waveguide surface is the blaze angle α _BA , α _BA is desirably an angle satisfying the expression (27).

_{Ncosα BA = n s (sinA 0} sinα BA + cosA 0 cosα BA) ...... (27) α BA: grating coupler blaze angle A _0: incident angle of the laser beam to the grating coupler N: effective refractive index of the optical waveguide n _s : Refractive index of optical integrated circuit board Here, the relationship between Λ and A ₀ is expressed by equation (28), and A ₀ is determined by determining Λ and the wavelength λ (0) of the semiconductor laser light, and from equation (27) α _BA is determined. Specific examples of α _BA The, Λ = 3μm, λ (0 ) = 0.78μm, N = 2.209, n s
In the case of = 2.2, it is about 14 degrees. In general, a blazed grating coupler can be formed by performing an ion milling technique and causing ions to be obliquely incident on a substrate for forming an optical integrated circuit. The error in making a blazed grating depends on the angle of incidence of ions in the ion milling technique. However, even if α _BA does not completely satisfy the expression (27), the effect is exhibited. For example, if the incidence coupling effect of a grating coupler with a rectangular cross section is 1, the incidence efficiency becomes more than twice when phrased, and even if the error of α _BA is ± 10%, the effect on the incidence efficiency is about 10%. Only to a degree.

The effect of the blazing of the grating coupler for incidence on the optical waveguide described above is similarly observed for the grating coupler for diffracting or emitting light from the optical waveguide into the substrate. FIG. 17 shows a grating coupler having a rectangular cross-sectional shape. By blazing the grating coupler as shown in FIG. 18, the efficiency of diffraction and emission to the substrate is dramatically improved. Optimal blaze angle α 'at this time
_BA is given by equation (29).

_{Ncosα BA '= n s (sinα} 0 sinα BA' + cosα 0 cosα BA ') ...... (29) α 0: the lattice spacing of the exit angle or diffraction angle grating coupler of the laser beam from the grating coupler lambda' and alpha ₀ Relationship Is expressed by equation (30), where Λ ′ is the wavelength λ of the semiconductor laser light.
By defining (0), α _BA ′ is determined.

In general, Λ and Λ 'are equal, so α _BA
And α _BA ′ are equal. In the case of a grating coupler having a rectangular cross-sectional shape, the relationship between the propagation vector of the optical waveguide light, the propagation vector of the diffracted light, and the lattice vector of the grating coupler cannot completely satisfy the Bragg condition. Or more), and as a result, the grating coupler does not become highly efficient. On the other hand, by blazing the cross-sectional shape of the grating coupler, diffraction generally occurs only in the vicinity of the Bragg condition, and the generation of high-order diffracted light is suppressed, and the efficiency of the grating coupler is approximately twice as high. Become. In general, the value of α _BA ′ is appropriate to be about 14 degrees,
_{As in} the case of _BA , even if the processing accuracy fluctuates about ± 2 degrees, the effect does not decrease so much. By blazing the grating coupler as described above, it is possible to dramatically increase the efficiency of coupling in and out of the optical waveguide.
The blazing of the grating coupler has no adverse effect on the aberration correcting grating of claims 1 to 7 of the present application.

Embodiment 7 FIG. 19 shows a seventh embodiment of the present invention, and shows an optical system of an optical head constituted by combining an optical integrated circuit and a bulk type optical element which is a conventional optical element. is there. No.
19A is a diagram of the optical system viewed from the side, and FIG. 19B is a diagram of the optical system viewed from the front. In the optical system shown in FIG. 19, 4 is a light source made of a semiconductor laser, 31 is a condenser lens for collimating light emitted from the semiconductor laser, 37 'is a photodetector for monitoring, and 30 is formed on the optical waveguide 2. Grating coupler 3,3 'SAW optical deflector 12 aberration correction grating 6,6'
An optical integrated circuit according to the present invention, 32 is a polarization beam splitter, 33 is a λ / 4 plate, 14 is a focusing lens for narrowing laser light to minute spot light, and 35 is for optical disk surface shake and the like. A voice coil 15 for moving the objective lens up and down so that the distance between the optical disc and the objective lens is always kept constant is an optical disc. The reflected light from the optical disk passes through the λ / 4 plate again, its deflection direction is changed, reflected by the polarizing beam splitter, collected by a convex lens, and then guided to a triangular prism 36 called a wedge. The light is split into two by the triangular prism 36 and the direction of the light is changed and guided to 37 quadrant photodetectors. The servo signal for the tracking servo of the optical disc is the difference between the sum of 37-1 and 37-2 and the sum of 37-3 and 37-4, and the servo signal for the focusing servo is 37-1 and 37-4. And 37−2,37
From the difference from the sum of -3, a reproduction signal for extracting the information of the disc can be obtained from the sum of 37-1, 37-2, 37-3, 37-4. This optical head has a feature that the micro tracking speed is high (the micro seek time is short) because the SAW light deflector 12 can perform the light deflection in the tracking direction. Further, since the return light is not returned to the optical waveguide, the light utilization efficiency is high.

[Embodiment 8] Fig. 20 shows an eighth embodiment of the present invention. As shown in Fig. 19, an optical head constituted by combining an optical integrated circuit of the present invention and a bulk type optical element which is a conventional optical element is used. 2 shows an optical system. FIG. 20 (a) is a diagram of the optical system viewed from the side, and FIG. 20 (b) is a diagram viewed from the front. The optical head shown in FIG. 20 differs from the optical head shown in FIG. 19 in that a glass block (prism) 24 for changing the optical path, a stop lens 14 and a voice coil 35 are separated from other optical systems. No.
The optical head shown in FIG. 19 needs to move the entire head optical system including the semiconductor laser when performing a macro seek, but the head shown in FIG. 20 uses only a glass block, a focusing lens, and a voice coil. The feature is that mass cross seek can be performed simply by incorporating and moving it in the course fukucheta 38. As a result, the movable portion of the head is small and lightweight, and the speed of macro seek can be improved. As a result, this head uses a SAW optical deflector and a small and lightweight head
Since the microseek time can be reduced at the same time, the configuration is effective as a high-speed access optical head.

Embodiment 9 FIG. 21 shows a ninth embodiment of the present invention, which is an improvement of the optical head of FIG. FIG. 21 (a) is a diagram of the optical system viewed from the side, and FIG. 21 (b) is a diagram viewed from the front. 20 is different from the head of FIG. 20 in that a notch is provided on the bottom surface of the optical integrated circuit substrate 1. The return light from the optical disk is reflected by the grating coupler without being incident thereon, and the light is reflected out of the substrate 1 from the notch. And receive it at the photodetector. In the grating coupler, the polarization directions of the outgoing light and the incident light are different due to the presence of the / 4λ plate 33. When the deflection directions are different, the effective refractive index N of the optical waveguide is different, so that the return light is totally reflected into the substrate without being coupled by the grating coupler. This method utilizes a difference in coupling efficiency of the grating coupler due to a difference in polarization direction, and has a feature that a deflection beam splitter is not required as compared with the method in FIG.

Embodiment 10 FIG. 22 shows an optical head compatible with a magneto-optical disk according to a tenth embodiment of the present invention. The present optical head is characterized in that, by changing the optical path of the return light, the return light does not enter the grating coupler and the light is emitted from the substrate. The difference between the forward and return optical paths can be caused, for example, by changing the inclination angle of the 6 'aberration correction grating or adjusting the angle of the rising prism.
The light reflected by the grating coupler 3 'is 1/2 of 39
After being incident on the λ plate and rotating the deflection direction, the light is converted into convergent light by the lens 35, and TE, T is detected by the photodetector 42 having the polarization separation film 40.
The light intensity is detected for each M-polarized light. The focus servo signal, the tracking servo signal, and the optical disk pit signal can be extracted from the sum and / or difference signals of the quadrant photodetectors 41, 41.

〔The invention's effect〕

As described above, by providing the aberration correction grating of the present invention, it is possible to prevent a decrease in the coupling-in and out-coupling efficiency of the grating coupler and aberrations such as chromatic aberration due to a wavelength variation of light, and thus, a multimode semiconductor laser can be used as a light source. In this case, an optical integrated circuit with less characteristic fluctuation can be formed. In addition, light use efficiency is high,
There is an effect that an optical head device having a high threshold value of optical damage, high light deflection efficiency, high-speed access, and a wide range in which the focusing servo and tracking servo mechanisms can effectively operate can be obtained. Further, the optical integrated circuit according to the present invention can be widely applied to various optoelectronic components such as an optical head for an optical disk device and an optical head for a laser beam printer.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of an optical integrated circuit according to the present invention, FIGS. 2 and 3 are cross-sectional views of an aberration correction grating used in the optical integrated circuit of the present invention, and FIG. FIG. 5 is a perspective view of an optical head for an optical disk device showing an embodiment, FIG. 5 is a manufacturing process diagram of an optical integrated circuit of the present invention, FIGS. 6 to 8 show a second embodiment of the present invention, and FIG. FIG. 7 is a perspective view showing an optical integrated circuit in which elements are hybrid-integrated, FIG. 7 is a perspective view showing a linear orthogonal coordinate system used for describing the embodiment, FIG. 8 is a perspective view showing a light deflecting effect by an optical deflector. FIG. 9 shows a third embodiment of the present invention, which is an optical integrated circuit in which a grating coupler and a Fresnel lens are combined, (a) is a sectional view, (b) is a plan view, and FIGS. FIG. 10 shows an optical head for an optical disk device showing a fourth embodiment of the present invention. FIG. 10 is a plan view of an optical integrated circuit; Fig. 12 shows the principle of detecting the focus error signal of the optical disk, Fig. 12 shows the principle of detecting the focus error signal of the optical disk, Fig. 12 shows the optical disk being in focus, Fig. 15 to 18 show a plan view showing the case after the focal point, showing a sixth embodiment of the present invention,
FIG. 15 is a cross-sectional view of an incident grating coupler having a rectangular grid shape, FIG. 16 is a cross-sectional view of an incident grating coupler having a blazed grid shape, and FIG. 17 is a cross-sectional view of an output grating coupler having a rectangular grid shape. FIG. 18 is a cross-sectional view of an emission grating coupler having a blazed grating shape, and FIG. 19 shows a seventh embodiment of the present invention, in which an optical head is formed by combining an optical integrated circuit and a bulk type optical element. (A) is a side view thereof, (b)
FIG. 20 is a plan view, FIG. 20 shows an eighth embodiment of the present invention, and shows an optical system of an optical head in which a part of an objective lens for detecting information on an optical disk is separated, (a) is a side view thereof, and (b) FIG. 21 shows a plan view, FIG. 21 shows a ninth embodiment of the present invention, and shows an optical head optical system of a type for returning reflected light from an optical disk to an optical integrated circuit again, (a) is a side view thereof, and (b) Is a plan view,
FIG. 22 shows a tenth embodiment of the present invention and is a side view showing an optical system of an optical head used in a magneto-optical disk drive. DESCRIPTION OF SYMBOLS 1 ... Substrate 2, 2 ... Optical waveguide, 3,3 '... Grating coupler, 4 ... Semiconductor laser, 5,5' ... Glass block, 6,6 '... Aberration correction grating, 7 ... Guided light , 8 ... substrate, 9 ... SiO ₂ , 10 ... reflective film, 11 ... collimating lens, 12 ... optical deflector, 13 ... glass block, 14 ... objective lens, 15 ... optical disk, 16 ... ... Condensing beam splitter, 17,17 '... Photodiode, 18 ... Buffer layer, 19 ... Resist, 20 ... Electron beam, 21 ... Focus, 22 ... Fresnel lens, 23 ... End face, 24 ... Condensing beam splitter, 25, 25 '... photodetector, 26 ... metal stage, 27 ... signal light, 28 ... incident side end face, 29 ... reflected light spot, 30 ... optical integrated circuit, 31 ... ... Condenser lens, 32 ... Polarization beam splitter, 33 ... λ / 4 plate, 34 ... Start-up mirror, 35 ... Voice Il, 36 ... Triangular prism, 37 ... 4 split photodetector, 37 '... Monitor photodetector, 38 ... Coarse actuator, 39 ... 1 / 2λ plate, 40 ... Polarization separating film, 41, 41 ': 4-split photodetector, 42: Photodetector, 43: Grating coupler.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Achichi Ito 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside the Hitachi, Ltd. Production Technology Laboratory Co., Ltd. (72) Takako Fukushima 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Inside Hitachi, Ltd. Production Technology Laboratory (72) Inventor Masataka Shiba 292, Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside Hitachi, Ltd. Production Technology Laboratory (72) Inventor Akira Arimoto 1-280, Higashi-Koigabo, Kokubunji-shi, Tokyo Central Research Laboratory, Hitachi, Ltd.

Claims (3)

(57) [Claims] In an optical integrated circuit in which a semiconductor laser is used as a light source and light emitted from the semiconductor laser is made incident on an optical waveguide, the blazed laser light incident grating coupler has an angle satisfying the following expression. Characteristic optical integrated circuit. N cos α _BA = n _s (sin A ₀ sin α _BA + cos A ₀ cos α _BA ) α _BA : Blaze angle of the grating coupler for laser beam incidence A ₀ : Incident angle of the laser beam on the grating coupler N: Optical waveguide Effective refractive index n _s : refractive index of optical integrated circuit board 2. An optical integrated circuit in which a semiconductor laser light is used as a light source and the laser light guided in the optical waveguide is emitted by a grating coupler, wherein the blaze angle of the grating coupler for emitting the blazed laser light is expressed by the following equation. An optical integrated circuit characterized by an angle satisfying the following. N cos α _BA '= _ns (sin α ₀ sin α _BA ' + cos α ₀ cos α _BA ') α _BA ': Blaze angle of grating coupler for laser beam incidence α ₀ : Incident angle of laser light to grating coupler N : Effective refractive index of optical waveguide n _s : Refractive index of optical integrated circuit board 3. A semiconductor laser as a light source, a collimator lens for converting light emitted from the semiconductor laser into parallel light, an optical waveguide formed on a dielectric substrate having an acousto-optic effect, and a device for causing light to enter the optical waveguide. Grating coupler, optical deflector using surface acoustic wave formed on optical waveguide, grating coupler for emitting deflected light from optical waveguide, aberration correction grating for correcting wavelength fluctuation of semiconductor laser light source, on optical disk An optical device having a lens provided with a focusing mechanism for condensing light, comprising: a photodetector for detecting reflected light from the optical disc through a notch formed in a bottom surface of a substrate. .